Method of preparing mix for producing refractory gas concrete and the product obtained thereby

ABSTRACT

Method of preparing a mix for producing refractory gas concrete containing powdered chrome-alumina slag and a high-alumina refractory material as fillers, comprising the mixing of constituents followed by adding a gas-developing agent. The resulting concrete is also subject of the invention.

AU 116 EX United States Patent 1191 Nekrasov et al.

1 Jan. 8, 1974 1 1 METHOD OF PREPARING MIX FOR PRODUCING REFRACTORY GASCONCRETE AND THE PRODUCT OBTAINED THEREBY 221 Filed: Feb. 18, I972 211Appl. No.: 227,623

[52] US. Cl 106/40 R, 106/75. 106/84. 106/87, 106/97 [51] Int. Cl.. C04b33/00, C0412 33/02, C04b 33/12 [58] Field of Search 106/40 R, 78, 87,106/75, 66

[56] References Cited UNITED STATES PATENTS 3,382,082 5/1968 Eubanks etal. 106/40 R 2,109,532 3/1938 Hill 106/87 2,915,802 12/1959 Dugas 106/873,700,470 10/1972 Barton 106/75 Primary Examiner-A. B. Curtis AssistantExaminer-Mark Bell Attorney-Eric l-l. Waters et a1.

[57] ABSTRACT Method of preparing a mix for producing refractory gasconcrete containing powdered chrome-alumina slag and a high-aluminarefractory material as fillers, comprising the mixing of constituentsfollowed by adding a gas-developing agent. The resulting concrete isalso subject of the invention.

4 Claims, No Drawings METHOD OF PREPARING MIX FOR PRODUCING REFRACTORYGAS CONCRETE AND THE PRODUCT OBTAINED THEREBY The present inventionrelates to a method of preparing a mix for producing refractory gasconcrete, and to the product thus obtained, which can find applicationin various branches of the economy, particularly, in the metallurgicalindustry as a material for heat insulation and lining of heat-treating,annealing and open-hearth furnaces where a temperature of up to l,200 Cis to be maintained.

Nowadays, for high-temperature insulation use is made of costly criticallightweight and ultra-lightweight refractories, as well as ofheat-insulation piece-articles. it proves difficult to run the work withthese materials on an industrial scale. Besides, lightweight refractorypiece-articles are manufactured by firing shaped pieces of materials,this involving additional cost and making the process of theirmanufacture more timeconsuming.

lt is therefore logical that the use of refractory gas concrete for theabove-mentioned purposes would be quite expedient.

However, so far known in the art is only a refractory gas concrete withan operating temperature of up to l,000 C, which is employed instead oflightweight refractories (or for heat insulation and lining of thermalunits operating at a temperature of up to l,000 C).

The method of producing such refractory gas concrete resides in that thecomponents of a binder whose composition includes sodium silicate(crushed soluble glass) and a component containing dicalcium silicateare mixed with a filler and water, and then a gasdeveloping agent isadded thereto.

As components containing dicalcium silicate, nepheline slurry,ferrochrome slag, or Portland cement can be used.

Chamotte is usually employed as a filler.

The refractory gas concrete produced from the mix prepared by the knownmethod features high fire shrinkage (up to 2%), and its maximumoperating temperature is l,000 C.

It is an object of the present invention to provide a method ofpreparing a mix for producing refractory gas concrete featuring highthermal resistance (up to l,200 C) and relatively low shrinkage (up to lpercent).

The invention also has as its object to provide refractory gas concreteof the kind here disclosed.

These and other objects of the invention are accomplished in that, whenpreparing a mix for producing refractory gas concrete on the basis of abinder containing sodium silicate and nepheline slurry or ferrochromeslag, by mixing the components of the binder with water and subsequentadding a gas-developing agent, use is made as a filler of powderedchrome-alumina slag taken in an amount of 22 to 32 percent of the totalweight of the mix and of a high-alumina refractory material taken in thesame amount.

The essence of the present invention is as follows.

Chrome-alumina slag which is a waste product of the aluminothermicprocess of producing metallic chromium features an ability of expandingwhen subjected to wet heat treatment, and therefore its utilization as afiller in a mix for preparing refractory gas concrete allows a reductionof shrinkage phenomena and an increase of the temperature at which thegas concrete can be employed.

An averaged chemical composition of the slag used is presented in Table1.

The use of the chrome-alumina slag alone as a filler in the refractorygas concrete makes possible the production of a gas concrete with astrength of 5 to 8 kg/cm; therefore for increasing the strengthcharacteristics of the refractory gas concrete a high-alumina refractorymaterial is introduced into the mix, which allows an increase in thestrength of the gas concrete to 12-20 kg per cm and an increase of thetemperature at which the gas concrete can operate.

A high-alumina powder prepared from wastes of broken high-aluminaarticles must contain not less than 62 percent of aluminum oxide.

Both the high-alumina refractory material and chrome-alumina slag mustbe ground to such a degree of fineness, that not less than 70 percent ofa sample should pass through a sieve with a mesh of 4,900 apertures percm.

The refractory and slag materials introduced into the gas concrete mixas fillers in the powdered state make it possible to obtain mixes with ahomogeneous structure, this being a very important factor for producingcellular concretes.

The refractory gas concrete produced from the mix prepared by thepresent method has the following physicomechanical properties:

a) operation temperature up to l,200C

b) ultimate compression strength after the maximum operating temperaturenot less than 12 to 20 kg/cm 0) additional shrinkage at operatingtemperature not higher than 1% d) volume mass not less than 500 to 800kg/m and over The cost of one ton of the refractory gas concrete with avolume mass of 600 kg/m is 30 roubles as against 100 to 900 roubles perton of the lightweight refractory material, in lieu of which the presentgas concrete can be used. Moreover, the present gas concrete is based oncheap and easily available materials, so that its use is expedient fromthe economical standpoint. The process of producing refractory gasconcrete practically does not differ from that of producing conventionalautoclave concrete.

A gas concrete mixer is started and then charged with water preheated to65 or C, an aqueous solution of sodium silicate and sodium hydroxide;then powdered materials are introduced into the mixer: chrome- 0 aluminaslag, high-alumina refractory, finely ground and the mix is allowed tostay in the moulds at this temperature for a period of 3 to hours.

After preliminary hardening of the articles, the hump is cut off fromthem, and the shaped articles are subjected to autoclave treatment byself-curing techniques.

With the help of electric heaters the temperature in the autoclave ismaintained within 170 to 180 C.

The steam which evolves in the autoclave builds up a pressure whichduring 3 hours reaches 8 gauge atmospheres and is maintained at thislevel for 4 hours. Then the pressure is relieved to 0 during a period of3 hours, and the gas concrete articles are removed from the autoclave.After that the articles are kept under shop conditions for 3 days at atemperature of C to complete readiness.

For a better understanding of the inventive method and product, givenhereinbelow are examples illustrating the compositions of the mix forrefractory gas concrete.

EXAMPLE 1 EXAMPLE 2 Composition of mix (in wt.%):

1. F iller: chrome-alumina slag 2 8 high-alumina refractory 28 Finelyground soluble glass 5.8 Nepheline slurry 8.1 Aluminum powder 0.20Sodium hydroxide 1.0 Aqueous solution of soluble glass with density of1.38 15.2 7. Water 13.7 The refractory gas concrete produced from saidmix features the following properties:

volume mass 600 kg/m operation temperature 1,200C ultimate compressionstrength after exposure to temperature of l,200C 16 kg/cm additionalshrinkage after exposure to temperature of EXAMPLE 3 Composition of mix(in wt.%):

1. Filler: chrome-alumina slag 32 high-alumina refractory 32 2. Finelyground soluble glass 6.9 3. Ferrochrome slag 4.2

4. Aluminum powder 0.10

5. Sodium hydroxide 0.8

6. Aqueous solution of soluble glass with density of 7. Water 11 Theresulting refractory gas concrete features the following properties:

volume mass 800 kg/m operation temperature 1,200C

ultimate compression strength after exposure to operation temperature l8kg/cm additional shrinkage after exposure to temperature of The strengthof the refractory gas concrete is such that this concrete can be usedinstead of lightweight refractory articles for high-temperatureinsulation and lining of furnaces and thermal units operating at atemperature of up to 1,200 C.

The refractory gas concrete is fit for manufacturing large-size blockstherefrom, so that the erection of thermal units can be run on anindustrial scale and the terms required for their construction can bereduced. Moreover, the use of the refractory gas concrete provides apossibility for developing most rational designs of furnaces, sincearticles of various configurations can be manufactured from thisconcrete. Experimental 1,000 m lots of the refractory gas concreteproduced on an industrial scale have shown that this concrete can bemass-produced with the use of equipment employed at the now existingplants engaged in producing conventional cellular concrete, thiscircumstance materially facilitating rapid large-scale application ofthe new products. Unlike conventional gas concrete, the refractory gasconcrete based on soluble glass can be subjected to hump removalprocedures 2 hours after pouring it into the moulds, whereby labourefficiency is increased three-fold.

Blocks manufactured from the refractory gas concrete, which were mountedin furnaces and thermal units of metallurgical plants, proved to bereliable in operation.

What we claim is:

1. A refractory gas concrete having high thermal resistance, namely upto 1,200 C, and low shrinkage, namely below 1 percent, comprising abinder including sodium silicate, a finely ground filler consisting ofchrome-alumina slag, in an amount of 22 to 32 percent of the totalweight when mixed with said binder with the addition of water, a finelyground high-alumina refractory material in the same amount, saidmaterial being prepared from wastes of broken high-alumina articlescontaining at least 62 percent aluminum oxide, and a gas-developingagent selected from the group consisting of sodium hydroxide andaluminum powder.

2. The refractory gas concrete as defined in claim 1, wherein saidbinder further includes nepheline slurry.

3. The refractory gas concrete as defined in claim 1, wherein saidbinder further includes ferrochrome slag.

4. A method of preparing a mix for producing refractory gas concrete,comprising the steps of: mixing with water a finely ground binder,including sodium silicate, a finely ground filler consisting of powderedchromealumina slag, and a high-alumina refractory material prepared fromwastes of broken high-alumina articles containing at least 62 percentaluminum oxide; and subsequently adding a gas-developing agent selectedfrom the group consisting of sodium hydroxide and aluminum powder.

2. The refractory gas concrete as defined in claim 1, wherein saidbinder further includes nepheline slurry.
 3. The refractory gas concreteas defined in claim 1, wherein said binder further includes ferrochromeslag.
 4. A method of preparing a mix for producing refractory gasconcrete, comprising the steps of: mixing with water a finely groundbinder, including sodium silicate, a finely ground filler consisting ofpowdered chrome-alumina slag, and a high-alumina refractory materialprepared from wastes of broken high-alumina articles containing at least62 percent aluminum oxide; and subsequently adding a gas-developingagent selected from the group consisting of sodium hydroxide andaluminum powder.